This proposal is concerned with the genetic control of embryogenesis in a simple higher organism. Our immediate objective is to develop new technology to rapidly assay for genes that control the production of specific cell lineages. This study is facilitated by the availability of conditional lethal mutants that block normal development at specific cell stages in embryogenesis. We propose to determine the cell stage when the function of a mutation is required. A microspectrophotometer and a flow microfluorometer will be employed to determine which mutants continue to synthesize DNA beyond their defective cell stage. Bio- and histochemical analysis of these mutants will elucidate the disappearance of a specific cell lineage. Isozymes found to be specific to a given cell lineage will be developed to rapidly assay for lineage mutants.